This invention relates to a composition and method for increasing the dissipation of heat from the surface to which the composition is applied and for shielding surfaces from heat. This invention is particularly useful in welding and brazing operations and in situations where heat sensitive materials must be protected from processes which temporarily employ high concentrations of thermal energy.
In many industrial and technical processes, high and intense concentrations of thermal energy in the form of flame, electrical resistance or discharge, laser, charged particle irradiation and other useful forms are often employed in a relatively confined space so that materials and work pieces cannot be readily and practically cooled by conventional means. This inability to dissipate and remove excess heat can limit production, produces undesirable effects and less than satisfactory results in certain operations, and may produce hazards that can result in damaged materials and fires. Particularly undesirable effects are excessive expansion or unsightly and unacceptable scorching or marring of metals or metal surfaces so that their utilization is significantly compromised.
Examples of specific processes where heat dissipation is of prime importance are welding operations and cutting operations with acetylene or electrical torches, especially the cutting and welding of the high melting point steels and similar alloys. Particularly, where costly alloys such as specialty stainless steels are used, distortions because of welding or cutting operations can be significantly costly. Other operations such as the sweating of copper pipes or tube joints in confined spaces near woodwork such as in the installation of water pipes in residential homes can present fire hazards with consequent endangerment of life and property. Accordingly, a principle object of the present invention is to provide a composition and method which will greatly reduce the aforementioned hazards and allow the performance of welding and brazing in locations and at speeds which are unattainable today.
Prior art approaches to solving the problem of heat dissipation have been to exercise extreme care in welding or brazing and to interrupt operations so that work pieces can cool down before they undesirably transfer heat to unwanted places. Another prior art approach has been to soak strips of fabric with a solution of fire retardants and apply these to the affected surface areas. However, it is difficult to position such strips and have them remain in effective contact with the surface to be cooled especially when the surface is vertical or inverted. Thus, it is another object of the present invention to provide a composition and method which can be used on surfaces in a wide variety of positions and configuration to cool them and dissipate heat.
Another prior art method has been to incorporate fire retardant chemicals into organic polymer slurries and spray or spread these onto the surface to be cooled. This method can be effective in terms of heat removal and flame retardation; but, once the water has evaporated from the polymer matrix the residue can react with the underlying metal surface, cause discoloration and unpleasant and unwanted smoke and vapors, and leave a residue that is difficult to remove. Accordingly, it is still another object of the present invention to provide a composition with sufficient heat absorbing capacity to cool a work piece in most operations without unpleasant and unsatisfactory vapors and residue.
Prior art compositions such as those disclosed in U.S. Pat. No. 5,035,951 to Dimanshteyn incorporate an inorganic aqueous coating which undergoes endothermic reactions when exposed to flame heat and acts as a thermal barrier up to about 2000xc2x0 F. The coating contains water soluable alkali metal silicates, a hydrated metal silicate clay, and an inorganic particulate material. Another flame retardant is disclosed in U.S. Pat. No. 5,518,638 to Bull et al wherein the composition described can be sprayed on surfaces for preventing fires and comprises an aqueous mix of silicates and bentonite with mineral additives as thickeners. U.S. Pat. No. 5,709,821 to Von Bonin et al discloses a fire resistant gel which can be used for preventing fire with or without drying and the gel contains aluminum salts, phosphorus compounds, a alkali metal salt, and up to about 85% water. In addition, U.S. Pat. No. 4,983,326 to Vandersall describes a process for mixing thickener, water and other additives with known liquid fire retardants to produce a material that is about ⅔ water. It is still a further object of the present invention to provide an improved gel composition with high water content which has improved and superior performance over previously known compositions.
The foregoing and other objects of the present invention will be understood and their solution appreciated by those skilled in the art after referring to the following summary of the invention and detailed description.
In one aspect, the present invention is the surprising discovery of a composition for increasing the dissipation of heat from a surface to which it is applied comprising 85% to 99.5% by weight of water and 15% to about 0.5% by weight of a magnesium silicate hectorite clay which forms a colloidal suspension gel when mixed with water. An especially preferred clay is laponite. The composition benefits from the adition of about 0.1% to about 1.0% by weight of an electrolyte which can be sodium nitrate for accelarating the thickening of the composition and from about 0.02% to about 0.06% by weight of the pyrophosphate salt as an inhibitor to aid in control of thickening the gel and, hence, the viscosity of the gel. (The more viscous gel may be referred to herein as a xe2x80x9cpastexe2x80x9d when appropriate.) About 0.5% to about 5% of a commercially known fire retardant is preferably added to achieve the most desirable form of the present invention.
In another aspect, the present invention is a composition comprising a minor portion of a magnesium silicate hectorite clay, a minor portion of a flame retardant, and a major portion of either distilled or de-ionized water wherein the composition is a translucent, thixotropic gel. In preparing said composition, still another aspect of the invention is the process wherein the laponite clay is first combined with water to produce a gel before addition of the fire suppressant which typically may include an inhibitor.
In still another aspect the present invention is a method of producing a composition for increasing the dissipation of heat from a surface to which it is applied comprising the steps of preparing a first mixture by blending water with about 0.5% to 3% by weight with a magnesium silicate hectorite clay to form a colloidal suspension said blending being performed with minimum agitation to reduce air entrapment. Sufficient electrolyte is added to accelerate the thickening process and a pyrophosphate salt is added as an inhibitor to control the thickening rate and final viscosity.
If the flame suppressant material contains an inhibitor the inhibitor may not be needed as an additive at this stage. A second mixture is prepared by mixing a commercially available fire suppressant with about 75% to 97% by weight of water and blending about 90% by weight of the first mixture with about 10% by weight of the second mixture using minimum agitation thereby producing a translucent, thixotropic gel.
In yet another aspect of the present invention is an improvement in the process for applying concentrated heat to a defined area on the surface of a high heat transfer material which is in contact with or adjacent to a region requiring protection from excessive heat by applying the aforementioned gel composition to the surface of the material at a point between the heated area and the region requiring protection whereby the heat applied is satisfactorily dissipated before being transferred to the protected region.
The gelled composition of the invention may preferably be applied in widths ranging from xe2x85x9xe2x80x3 to 3xe2x80x3 and in depths in the range of {fraction (1/16)}xe2x80x3 to xc2xdxe2x80x3 to a metal surface before welding or cutting and thereby preventing and/or reducing distortion of the metal from the heat of welding or of cutting the metal. The composition, because of its high water content and close contact with the underlying surface, dissipates and removes the excess heat by means of the evaporation of the water which is quite effective in reducing the heat transference along the metal surface beyond the point of application of the gel. In this respect it acts as an excellent heat sink and/or thermal barrier and rapidly and effectively dissipates heat.
In a further aspect, the present invention can act as a shield to direct flame. When coated onto a surface and subsequently direct flame is applied, the gel or paste will initially protect the underlying surface as water is evaporated from the gel. Continued application of heat will cause the gel to form a heat reflective crust which, for a period of time, will continue to protect the surface by reflecting heat away. This crust is principally formed by the fire suppressant in the gel.